The film is set in Fort de France, Martinique, under the Vichy regime in the summer of 1940. In this exotic location, world-weary fishing-boat captain Harry Morgan (Humphrey Bogart) is urged to help the French Resistance smuggle some people onto the island. He refuses, until the client, Johnson (Walter Sande), who has been hiring out his fishing boat (and owes him $825), is shot before paying him. Gerard, the hotel owner commonly known as Frenchy (Marcel Dalio), asks Harry to rent him his boat for one night to transport some members of the resistance. Broke, Harry ends up smuggling Helene (Dolores Moran) and Paul de Bursac (Walter Surovy). Meanwhile, a romance develops between Harry and Marie ("Slim") Browning (Lauren Bacall), an American wanderer who has come to the island.